All of the geometry functions need tests. 
I've been trying to compile a list of functions that need tests. Many of these are indirectly tested through the  DRC tests, but that isn't really as thorough as it ought to be.
-  search.c - 
-  IsPointOnLine 
-  IsPointOnPin 
-  IsPointOnArc 
-  IsPointOnLineEnd 
-  IsLineInRectangle 
-  IsLineInQuadrangle 
-  IsArcInRectangle 
-  IsPointInPad 
-  IsPointInBox 
 
-  find.c - 
-  LineLineIntersect 
-  LineArcIntersect 
-  PinLineIntersect 
-  LinePadIntersect 
-  ArcPadIntersect 
-  ArcArcIntersect 
-  IsRatPointOnLineEnd 
-  IsArcInPolygon 
-  IsLineInPolygon 
-  IsPadInPolygon 
-  IsPolygonInPolygon 
-  IS_PV_ON_RAT 
-  IS_PV_ON_ARC 
-  IS_PV_ON_PAD 
 
-  polygon.c